Modulated short arc lamp envelope structure



Oct. 24, 1961 N. c. BEESE 3,005,923

MODULATED SHORT ARC LAMP ENVELOPE STRUCTURE Filed June 29. 1959 INVEN TOR. NORMAN C. BEESE TTORNEY United States Patent 3,005,923 MODULATED SHORT ARC LAMP ENVELOPE STRUCTURE Norman C. Beese, Verona, NJ assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed June 29, 1959, Ser. No. 823,789 1 Claim. (Cl. 313-484) This invention relates to electrical discharge lamps and more particularly to envelope structure for modulated short are lamps having good acoustical resonance properties.

Alternating or direct current are lamps, when modulated by alternating currents, will possess certain critical or resonant frequencies which are dependent upon the geometrical construction of the tube, the ionizable gas or vapor employed and the operating conditions under which the lamp is used. The gases may be the rare inert monatomic gases such as argon, xenon, etc., and the vaporizable metals may be mercury, cadmium, zinc, thallium, etc.

If a resonant frequency of sufficient intensity is used to operate or modulate the arc, the sound energy pro duced therein and reflected about the arc chamber adversely affects the character of the discharge and may extinguish the arc, or the lamp envelope may be caused to blow up.

When a modulated arc lamp is used to transmit various forms of intelligence, such, for example, as in Wireless telephone systems using a searchlight beam to carry the modulated light signals, a source of radiation of high intensity is required resulting in operating temperatures approaching 1300" C. The envelope, therefore, is customarily formed of quartz or a vitreous material having a high silica content to withstand the high operating temperatures. However, unless the envelope structure is designed to withstand acoustical resonance resulting from resonant frequency modulated arcs, physical failure of the envelope will occur or its life seriously shortened.

Accordingly, it is a broad object of the present inven tion to provide an envelope structure for electrical discharge devices of the above type having good acoustical resonance properties therein.

Another object of the invention is to provide a novel envelope structure for electrical discharge devices of the above type capable of long life even when the discharge is modulated by intense resonant frequencies.

Other objects of the invention will become herein ap parent from the following detailed description wherein:

FIG. 1 is a longitudinal sectional view of an arc lamp showing one embodiment of the invention;

FIG. 2 is a similar view of another embodiment of the invention.

Referring to FIG. l, a gaseous discharge device such as a short are vapor lamp is generally designated by the reference 10. This lamp is comprised of a discharge section 12 and end sections 14-44 toprovide a sealed envelope or housing. The end portions 14-14 contain respectively lead-in conductors 16-16 which are formed of molybdenum or tungsten and terminate as shown in electrodes 18 and 20. The discharge section 12 is preferably made from clear fused silica or a similar vitreous material of high softening point and its preferably has a thickness of at least three millimeters so that it will safely Withstand the high filling and operating pressures common in such lamps. The end sections 14-44 are formed integrally of the same material and have the lead-in conductors 16-16' hermetically embeded in axial passageways 22--22' so that the electrodes 18 and 20 the electrodes 18 and 20.

2 are disposed within the discharge section 12 in the desired spaced relation to provide a gap 24 therebetween.

The lamp 10' is provided with a sealing tip, not shown, through which it is thoroughly degassed during the exhaust procedure and filled with a vaporizable material like mercury and/or a rare gas like xenon or krypton under a pressure of several atmospheres. As is customany in short are lamps, only a limited quantity of mercury, for example, is filled into the discharge vessel which is entirely vaporized under operating conditions of the lamp. When a source of electrical currents, for instance, an alternating current line voltage of volts is connccted to the lead-in conductors 16-16 of the lamp across a suitable ballast, an arc discharge is generated between the tips of electrodes 18 and 20, which assumes a very high brightness and absorbs a considerable Watt-age with the resultant heating of the discharge section 12 and the end sections 14-14. These sections normally resist the high temperatures and pressures, but if a resonant frequency is used to operate or modulate the are discharge, the refiected sound energy within the discharge chamber 22 builds up to such intensity that distortion, instability or even extinction of the are results and the siliceous discharge section may be caused to shatter. Therefore, in accordance with the invention, the electrodes 18 and 20 are relatively arranged so that the arc is caused to be dicharged at a point indicated at 24, which point is off the geometrical center of the discharge section. The distance off the geometric center of the point 24 is represented by the difference between the length of lines A and B and results in a defocusing of the sound energy produced by the arcing. No critical location of the point 24 is required other than that it be some substantial distance off the geometric center of the lamp 10. By preference, one of the electrodes or cathode 18 has a tapered face while the other electrode or anode 20- has an obtuse face.

In FIG. 2, a second embodiment of the invention is shown. In addition to the arrangement for off-center arc discharge, the vessel itself is asyrrnnetrical and formed with an irregular contour providing an enlarged annular circumferential zone about the are 24 formed between The off-center arcing and asymmetrical design of the lamp 10 markedly defocuses the sound waves created therein and thus effectively prevents extinction of the are or fracturing of the siliceous vessel.

. Modulated short are lamps having an envelope structure similar to that depicted in FIG. 1 but with central arcing and operated on a direct current of 20 amperes with superimposed alternating current modulation resulted in extinguishment of the arc with audio frequency resonance energies of 6, 12 and 18 kilocycles per second. At lower currents of 13.5 amperes, the critical or resonant frequencies which destroyed the arc were found to be at 5500, 11,000 and 16,500 cycles per second. When the off-center arcing in envelope structures of FIGS. 1 and 2. were employed under identical conditions, only slight distortion of the arc occurred.

It should be understood that the foregoing disclosure shows only preferred embodiments of the invention and that it intended to cover all modifications of the embodiments herein described which do not depart from the invention.

What is claimed is:

A high pressure electric discharge lamp comprising a. cylindrical light transmissive envelope having sealed ends and forming a discharge cavity therebetween, a gas filling said cavity, a first electrical conductor extending axially from one end of the envelope and having an electrode positioned within the discharge cavity, a second a 2k electrical conductor extending axially from the other end providing a circumferential space thereabout whereby of the envelope and having an electrode positioned withsound waves created within the cavity are defocused to in the discharge cavity to provide an arcing gap with the Provide for stability of operaticmfirst mentioned electrode, one of the conductor and electrode structures extending from one end of the envelope 5 References Citadel the file of thls patent a greater distance than the other conductor and electrode UNITED STATES PATENTS structure extends from the other end of the envelope t 2,678,408 Roberts May 11, 1954 locate the arcing gap ofif the geometrical center of the 2,728,871 Morin Dec. 27, 1955 discharge cavity and said cylindrical envelope having an 2,887,603 Haidinger May -19, 1959 enlarged diameter portion embracing the arcing gap and 10 2,896,107 Anderson July 21, 1959 

